The present invention relates to a turbocharger for a motor vehicle.
A turbocharger of the type emerges for example, from DE 10 2012 212 738 A1.
A turbocharger of the type has a compressor to which there is connected, at the suction side, a feed duct in the form of a suction pipe for charge air to be compressed and, at the pressure side, a pressure duct in the form of a pressure pipe for the compressed air. Furthermore, in the case of such turbochargers, there is normally additionally provided a bypass duct which connects the suction side to the pressure side. In the bypass duct, there is integrated a so-called overrun air recirculation valve for the controlled opening and closure of the bypass duct. The overrun air recirculation valve serves for pressure equalization and for preventing so-called pressure pulsation fluctuations. This is necessary, in particular, in the event of rapid load alterations, in particular load dumping, for example as a result of closure of the throttle flap, because, owing to the inertia of the compressor, a very high mass flow continues to be compressed for a short period of time, but is no longer taken in by the engine. This would result in the highly compressed charge air being repelled counter to the actual delivery direction.
Here, the charge air that is recirculated by the bypass duct may lead to undesired flow noises.
In DE 10 2012 212 738 A1, a diffuser as a separate component is provided in the inlet region, that is to say in the region in which the feed duct is connected to the compressor, which diffuser has, at the circumference, a multiplicity of flow openings by means of which a connection in terms of flow to the bypass duct can be realized.
The diffuser of the type can, however, result, during normal operation of the turbocharger, in pressure losses in the inflow of the charge air to be compressed.
Thus, it is the object of the invention to improve a turbocharger of the type for a motor vehicle with regard to the greatest possible pressure losses.
This and other objects are achieved in accordance with embodiments of the invention. A turbocharger includes a compressor and a suction-side feed duct, in the form of a suction pipe, for the charge air to be compressed. The charge air flows, during operation, in a flow direction to the compressor. Here, the feed duct is connected, in an inlet region, to the compressor. Furthermore, the turbocharger includes a pressure-side pressure duct, which is in particular in the form of a pressure pipe, for the compressed charge air. Furthermore, a bypass duct is formed which connects the feed duct to the pressure duct. For this purpose, at least one flow opening is formed on the circumference in the inlet region. Furthermore, the turbocharger includes an, in particular, electrically actuated overrun air recirculation valve for the controlled opening and closure of the bypass duct. It is also of particular importance that a flow-guiding element is situated in the feed duct upstream of the at least one flow opening in the flow direction, which flow-guiding element is formed and/or arranged such that an area of reduced pressure—in relation to the normal pressure of the charge air in a central region of the feed duct in the inlet region—forms at the flow opening during operation.
By way of this measure, it is therefore achieved that a relatively low pressure, in particular a flow dead zone, is formed directly at at least one flow opening, such that the charge air thus does not flow directly past the flow openings. Specifically, tests have shown that, in the case of the normal throughflow of the charge air at the flow openings, turbulence arises which then leads to undesired pressure losses. Such turbulence would also lead to undesired flow noises. By way of the measure described here, it is thus firstly the case that the pressure loss is kept low, and secondly, flow noise is also prevented or at least reduced.
It is preferable for multiple flow openings to be formed so as to be distributed over the circumference, such that altogether an adequately large flow cross section is formed and the charge air can flow uniformly back into the inlet region when the overrun air recirculation valve is open.
Here, the flow openings are preferably arranged only on a single, common circumferential line. They are therefore not spaced apart from one another or distributed in a flow direction. This makes it possible in a simple manner in terms of construction to form the desired flow dead zone for all flow openings.
In a preferred embodiment, the flow-guiding element has in this case a separation edge for the charge air to be compressed. Therefore, in particular, an abrupt cross-sectional widening for the charge air to be compressed is formed in the region of the flow-guiding element, such that, as viewed in the flow direction, the dead zone forms directly downstream of the separation edge. The at least one flow opening is correspondingly also arranged in the region immediately downstream of the separation edge.
The separation edge is preferably of encircling form, that is to say the flow-guiding element is preferably in the form of an encircling ring-shaped element.
In a preferred refinement, the flow-guiding element is in this case formed as a flow obstruction which narrows a flow cross section of the inlet region. In this embodiment, therefore, it is, in particular, the case that an encircling ring-shaped element is inserted in a simple manner into the inlet region directly upstream of the flow openings. Although this reduces the overall flow cross section, the positive effect of the elimination of turbulence at the flow openings is however predominant.
As an alternative to the arrangement of the flow-guiding element in the form of a flow obstruction, it is, however, also possible for the flow cross section to be widened, for example by virtue of a radial widening with an enlarged flow cross section in relation to the feed duct being formed in the inlet region.
For a more comprehensive reduction of possible pressure losses, it is the case in a preferred refinement that the flow-guiding element, which is in particular in the form of a flow obstruction, is not of continuous form as viewed in the circumferential direction. Therefore, instead of a continuous ring, multiple flow-guiding elements are formed so as to be distributed over the circumference, which flow-guiding elements are in each case spaced apart from one another in the circumferential direction. The flow radius of the feed duct is therefore maintained in the region of the spacings. Here, the flow-guiding elements arranged so as to be distributed in the circumferential direction are in each case positioned immediately upstream of at least one suction opening or else of a group of flow openings such that, in turn, the desired dead zone is formed at each flow opening.
Here, in a preferred embodiment, a separate flow-guiding element is assigned, in the manner of a flow obstruction, to each flow opening. Here, the flow-guiding element preferably projects radially inward and is formed in particular in the manner of a nose or generally in approximately a wedge shape. The flow-guiding element has a separation edge on the end side. In each case one flow opening is then arranged downstream of the nose.
Furthermore, the separation edge is preferably of curved form and has, in particular, an identical or at least substantially identical curvature to the flow opening. In this way, an arrangement of the flow opening directly downstream of the nose is promoted. A curved face surface, which is at the rear side as viewed in the flow direction, of the nose merges in a preferably flush manner in the radial direction into the flow opening.
The flow openings arranged so as to be distributed around the circumference are preferably connected to an encircling ring-shaped duct which is then adjoined by a suction-side subsection of the bypass duct. Thus, during operation, for example when the throttle flap is closed, charge air flows from the pressure side via the ring-shaped duct through the flow openings to the suction side (low-pressure side). The bypass duct may generally be divided into a suction-side subsection and a pressure-side subsection. The pressure-side subsection is formed between the overrun air recirculation valve and the pressure side, and the suction-side subsection is formed between the overrun air recirculation valve and the suction side.
In a preferred embodiment, it is furthermore the case that no flow opening is formed in the region in which the suction-side subsection opens into the ring-shaped duct. This promotes an efficient and uniform distribution of the recirculated charge air.
In general, the feed duct has, on an end side, an inlet connector by way of which it is fastened to the compressor. The inlet connector forms in this case the inlet region with the at least one flow opening and the flow-guiding element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.